Wherever reference is made hereafter in the description of the invention to a cage of a radiation-crosslinkable plastics material or to a method for producing a cage, it is understood that, instead of the cage, the invention also applies to a bearing part, for example a bearing ring of a rolling or sliding bearing or a sliding lining of a sliding bearing or a lining of a slideway of a rolling bearing or a plastic seal, for example for a bearing, or a plastic part in general.
In the production of a cage for a bearing, the irradiation with high-energy ionizing radiation, for example with x-ray or UV radiation or by means of particle radiation (such as for example beta radiation) brings about a chemical crosslinkage of the material of the body of the cage, which as a result of the irradiation is improved significantly with respect to the resistance to wear. It proves to be difficult in practice without additional aids to determine whether a sufficient pretreatment of the material of the cage by irradiation has taken place. The lack of a possible means by which the state of the irradiation of the plastics material can be detected in a simple way, in particular under the conditions of mass production, is currently making it more difficult to produce cages or generally plastic parts from a radiation-crosslinkable plastics material. In production, complex, expensive measures are required in the process sequence to be able to establish with certainty whether the plastics material has been irradiated.
It is known from DE 10 2004 053 376 A1 and the documents cited therein as well as from JP 08276506 AA (Abstract) to add laser-sensitive pigments to a plastics material, so that the plastics material provided with the pigments is given a marking or inscription during the laser treatment.
It is also known, for example from DE 103 51 813 B4 or else DE 103 51 812 B4, to activate plastics materials such as PTFE by means of ionizing radiation in order to couple to the activated plastics material organic molecules such as polyamide, and thereby form a covalent bond.
EP 0 644 344 B1 describes a method for producing a cage of a rolling bearing that receives rolling bodies, the body of the cage being produced from a plastics material that can be crosslinked when exposed to radiation, in particular when exposed to beta radiation, and the body of the cage being fitted with rolling bodies during the further course of the method. When carrying out the method, it is provided that the produced body of the cage is first fitted with the rolling bodies and then exposed to the radiation. It proves to be disadvantageous here that the rolling bodies received in the body partially shield the adjacent region of the body from the radiation, so that, specifically in the vicinity of the rolling bodies, the strengthening of the body is incomplete. No matter whether the cage is fitted with the rolling bodies before or after the irradiation, it is not evident from the appearance of the body whether the irradiation has taken place. The production of radiation-crosslinkable plastic cages therefore requires sophisticated quality control. Furthermore, it is envisaged to use for the irradiation a dose that is chosen rather too high, in order to ensure that the cages are completely crosslinked, and therefore strengthened, along the entire body. This is counter to a requirement for lowest possible radiation exposure.